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We changed our pads with non-vauxhall ones which means the brake pad sensors are not used and because of this the brake pad warning is displayed. A friend told us to wrap the 2 sensor wires (on each sided) together and the warning should go off.Tried it and it didn't.
Oh dear! Yet more dis-information. Neither OEM nor pattern pads come with sensing wires fixed to the pads. (I know that Fords of the early 80's came with or without wires embedded in to the pads - maybe you had a Ford of the early 80's :-/) If you were to look through the many many repeated questions & their answers you'll find that the sensor wire(s) are completely seperate from the pads. One end clips onto the butterfly anti-rattle clip fixed to the pads & the other plugs in under the front wing. If you bare the wires to a 'used' sensor & short the 2 ends together it WILL fool the brake pad check system.
Tried it and it DID 
Unfortunately in your case you don't really know if the pads have been changed or not.
You could buy some Vauxhall ones and get them changed just to be on the safe side.
How about checking them the old fashioned way and remove the wheel & have a proper look at both pads! That way you'll really know if they've been changed! :-?
The last time my low pad warning check was displayed I'd still at least half of each pad left.